From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754100AbdEEMv7 (ORCPT ); Fri, 5 May 2017 08:51:59 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:49468 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753740AbdEEMv4 (ORCPT ); Fri, 5 May 2017 08:51:56 -0400 Subject: Re: [PATCH v8 1/5] x86: add simple udelay calibration To: Lu Baolu , Greg Kroah-Hartman , Ingo Molnar References: <1490083293-3792-1-git-send-email-baolu.lu@linux.intel.com> <1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com> <590C1084.7010302@linux.intel.com> Cc: Mathias Nyman , tglx@linutronix.de, peterz@infradead.org, linux-usb@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Juergen Gross , xen-devel From: Boris Ostrovsky Message-ID: Date: Fri, 5 May 2017 08:50:34 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <590C1084.7010302@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/05/2017 01:41 AM, Lu Baolu wrote: > Hi, > > On 05/03/2017 06:38 AM, Boris Ostrovsky wrote: >> On 03/21/2017 04:01 AM, Lu Baolu wrote: >>> Add a simple udelay calibration in x86 architecture-specific >>> boot-time initializations. This will get a workable estimate >>> for loops_per_jiffy. Hence, udelay() could be used after this >>> initialization. >> This breaks Xen PV guests since at this point, and until >> x86_init.paging.pagetable_init() which is when pvclock_vcpu_time_info is >> mapped, they cannot access pvclock. >> >> Is it reasonable to do this before tsc_init() is called? (The failure >> has nothing to do with tsc_init(), really --- it's just that it is >> called late enough that Xen PV guests get properly initialized.) If it >> is, would it be possible to move simple_udelay_calibration() after >> x86_init.paging.pagetable_init()? > This is currently only used for bare metal. How about by-pass it > for Xen PV guests? It is fixed this for Xen PV guests now (in the sense that we don't crash anymore) but my question is still whether this is not too early. Besides tsc_init() (which might not be important here), at the time when simple_udelay_calibration() is invoked we haven't yet called: * kvmclock_init(), which sets calibration routines for KVM * init_hypervisor_platform(), which sets calibration routines for vmware and Xen HVM * x86_init.paging.pagetable_init(), which sets calibration routines for Xen PV -boris > > Best regards, > Lu Baolu > >> -boris >> >> >>> Cc: Ingo Molnar >>> Cc: x86@kernel.org >>> Signed-off-by: Lu Baolu >>> --- >>> arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++ >>> 1 file changed, 22 insertions(+) >>> >>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c >>> index 4bf0c89..e70204e 100644 >>> --- a/arch/x86/kernel/setup.c >>> +++ b/arch/x86/kernel/setup.c >>> @@ -837,6 +837,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p) >>> return 0; >>> } >>> >>> +static void __init simple_udelay_calibration(void) >>> +{ >>> + unsigned int tsc_khz, cpu_khz; >>> + unsigned long lpj; >>> + >>> + if (!boot_cpu_has(X86_FEATURE_TSC)) >>> + return; >>> + >>> + cpu_khz = x86_platform.calibrate_cpu(); >>> + tsc_khz = x86_platform.calibrate_tsc(); >>> + >>> + tsc_khz = tsc_khz ? : cpu_khz; >>> + if (!tsc_khz) >>> + return; >>> + >>> + lpj = tsc_khz * 1000; >>> + do_div(lpj, HZ); >>> + loops_per_jiffy = lpj; >>> +} >>> + >>> /* >>> * Determine if we were loaded by an EFI loader. If so, then we have also been >>> * passed the efi memmap, systab, etc., so we should use these data structures >>> @@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p) >>> */ >>> x86_configure_nx(); >>> >>> + simple_udelay_calibration(); >>> + >>> parse_early_param(); >>> >>> #ifdef CONFIG_MEMORY_HOTPLUG